''The catalyst was a three-car accident. How that happened I don't know,'' said Deputy Chief of Traffic Robert Kreuser. ''From there it was a chain- reaction. It just piled up.''

The crash killed at least three people, said police Capt. Larry Gille, who was coordinating rescue efforts in the northbound lanes of the Tower Drive Bridge on Interstate 43, which spans the Fox River.

At least 24 people were treated at the city's two hospital emergency rooms and three were admitted, officials said.

''It looks like it was exploding gas tanks from cars'' that caused the fire, Gille said. Firefighters extinguished at least one burning vehicle near near an oil company tanker trunk near the head of the pileup, witnesses said.

''It's a matter of unpiling the cars and treating the injured,'' Kreuser said.

Many of the injured had to be extricated from their cars. Police, firefighters, ambulance and rescue crews - including a crane - were dispatched to the bridge shortly after the accident was reported at 6:45 a.m.

''Somebody said it's something you'd see in a Los Angeles pile-up. It'll take a long time to see this thing out,'' police Lt. Roy Johnson said.

Minutes after the crash, dazed, bloodied drivers wandered in the roadway near the crash site. Other victims lay on the ground near the crest of the bridge, where other motorists went to help them.

Twenty yards away, just east of the bridge's superstructure, both northbound lanes were blocked by wreckage, some of it on fire.

Leo Terry of Green Bay, his face smeared with blood, said he was driving across the bridge when he entered a wall of fog, then slammed into a car stopped in front of him. ''You couldn't see nothing,'' he said.

James Vandertie, 19, who escaped with a few fragments of glass in his hand, said the chain reaction started when a van hit an oil tanker. ''It was like boom, boom, boom, every couple of seconds,'' he said.

Barbara Brandstatter of Red Banks said she was driving south across the bridge when she saw the wreckage on the opposite side.

She said the crest of the bridge had fair visibility at the time of the accident, but another wall of fog was just beyond where she stopped her car and set out flares.

Traffic chief Kreuser said the accident was the worst he'd seen in 28 years with the Green Bay department. ''We've never had anything of this magnitude.''

Green Bay, a city of 90,000 about 117 miles north of Milwaukee, is widely known for its National Football League team, the Green Bay Packers.